It is well known that a vehicle can coast during running only depending on its own inertias without using any engine power. In the meantime, the engine may consume only little fuel for ensuring its idling. Thus, the vehicle coasting is a significant mode for saving fuel.
When a vehicle is running, according to Newtonian mechanics, the traction outputted by the engine can make the vehicle accelerated. During the movement, resistances on vehicle, such as wind resistances, increase as the vehicle velocity increases, until they balance the traction outputted by the engine. The vehicle is at last in uniform motion. When a driver releases the accelerator, the vehicle slows down due to the resistances, generally complying with the simplified formula as follows,R1+R2=ma; R2=KμWherein, R1 represents the wind resistance and the friction resistance; R2 represents the resistance produced by the vehicle power and transmission assembly; K is a gear coefficient, and the higher the gear is, the bigger K is, and the lower the gear is, the smaller K is; This is the reason why the coasting distance is rather longer while the vehicle is running at higher gears, and inversely shorter while running at lower gear; μ represents the damping of the vehicle power and transmission assembly. If the vehicle coasts without connecting the power and transmission assembly, as known from this formula, resistances on vehicle will become smaller, and the vehicle can coast a longer distance and thus can save more fuel.
In the known prior art, for example the Chinese patent ZL 02282639.4, an overrunning clutch is installed in the vehicle transmission system. When the vehicle decelerates, it is out of the engine damping via overrunning clutch in order to coast without the engine damping, and thus the purpose for saving fuel is attained. There is a serious safety problem in this technical scheme because the vehicle is correspondingly in the neutral coasting state. When the vehicle is braked suddenly, the deserved and necessary power assisted brake for braking system deteriorates due to the overrunning clutch relation between the engine and wheels, which affects the driving safety significantly. Additionally, when a driver puts back the accelerator, although the overrunning clutch makes the vehicle out of the engine damping, the engine is not in idle fuel supply state since the accelerator does not return, but still consumes more fuel than in idle fuel supply state. Therefore, ideal fuel saving effects can not be achieved in this known prior art. Furthermore, the vehicle equipped only with this device can not move backward.
The fuel supply to the engine is divided to two parts: one is the idle fuel supply for keeping the engine idling, another is the accelerating fuel supply controlled by the accelerator pedal. Both kinds of fuel supply can be fed not only by one fuel line, but also by several lines.